Slide vanes, more specifically rotary slide vanes, are known and utilized by default in hydraulic power steering. These slide vanes control the hydraulic pressure and, as a result thereof, the steering assistance on an assistance cylinder as a function of the steering torque applied by the driver. In most cases, rotary slide vanes are utilized wherein an input shaft connected to a steering wheel via a steering column rotates relative to a control sleeve that is connected to the output shaft and to a steering pinion in the case of rack steering. Through a torsion system between the input shaft and the control sleeve, a torque-dependent angle of rotation of the vane and, as a result thereof a torque-dependent vane characteristic line, are realized. Accordingly, the rotation of the input shaft relative to the control sleeve serves to determine the assistance force needed for steering.
Rotary slide vanes for auxiliary force steering usually contain two vane elements that are disposed for coaxial movement inside each other and for limited rotational movement relative to each other for achieving a control path. Accordingly, the input shaft can be connected to a first vane element configured to be a rotary slide vane located radially inside. The control sleeve is radially disposed outside of, and surrounds, the first vane element. Both vane elements comprise control grooves that extend axially along at least a portion of the vane elements. The control grooves serve to control or move a pressure means from or toward working spaces of a hydraulic actuating power unit or servo motor. The control grooves however may also be disposed directly on the input shaft.
Such type rotary vanes are described in DE 10 2004 034 026 A1, DE 692 08 261 T2 and DE 197 55 633 A1 for example.
For flawless function of the rotary slide vane, precise manufacturing of the control edges and the control grooves is absolutely necessary. By designing the control edges accordingly, the opening cross section of the rotary slide vane can be dictated as a function of the angle of rotation between the vane elements. For this reason, manufacturing of the control edges requires complex and cost-intensive manufacturing methods. It is precisely the manufacturing of the control grooves running in the axial direction, in particular also described in the printed documents mentioned, that involves considerable expense. In particular the longitudinal grooves of the control sleeve, which lie inside, place increased demands on the manufacturing process. For example, the control grooves are manufactured by scraping and milling, whilst the corresponding geometry of the control edges is provided by stamping and grinding.
Another disadvantage of known rotary slide vanes is that they do not allow for implementing certain functionalities comprising electrically assisted power steering using hydraulically assisted power steering. This applies for example to functions in which the steering torque is not applied by the driver but by an electric motor. Such a functionality is for example needed for realizing parking assistance systems wherein the vehicle is parked automatically without the driver having to apply a steering torque. Applying a steering torque is hardly possible or only at considerable expense using a hydraulically assisted system having the described rotary slide vanes.